In some telecommunication networks, span powering is used when a power supply located at a service provider site, such as a central office, furnishes power to a remote site. Typically, a service provider furnishes power to equipment at the remote site near the customer premise from the power supply at the service provider site. In some communications networks, a pair of wires, often referred to as the copper twisted pair, couples both a communications signal and the power supply energy from the service provider site to the remote site. In other telecommunications systems, the twisted pair of wires serves only as an electrical path for coupling power from the service provider site to the remote site.
When span powering a remote DS1 device, for example, a DS1 power supply at the local site furnishes, via the twisted wire pair, a desired current and voltage to the remote site for powering a DS1 device. In some applications, it is desired to span power a DS3 NIU located at a remote site from the local site over twisted pair. Because of the differences in power requirements between the DS1 and DS3 devices, a power supply capable of powering a DS3 device must be used at the local site. A DS1 span power supply does not have the appropriate output to power a DS3 device. Hence, for span powering, a local DS1 power supply is required for a DS1 communications connection and a local DS3 power supply is required to span power a DS3 NIU. These power supplies are not interchangeable.
The assignee of the instant application, ADTRAN, Inc., designs and manufactures a Span Power and Protection Module (SPPM) that receives and isolates up to 28 DS1 signals, combines these signals with isolated T1-style (60 mA regulated) span power, and couples the combined span power/DS1 signal to traditional copper, twisted pair telephone line to power and drive a DS1 Network Interface Unit (DS1 NIU). In this SPPM, the T1 style span power is generated by 28 identical isolated span power supplies, which regulate their respective output currents to a nominal 60 mA, in one non-limiting example. This value is held in conjunction with the DS1 network interface units that terminate their span power input with a shunt device, for example, a zener diode to define the NIU operating voltage.
As noted before, the SPPM provides DS1 span power capability, but is not capable to span power a DS3 NIU. The powering requirements for a DS3 NIU are substantially different than those of a DS1 NIU. DS3 NIUs are typically powered using a constant voltage instead of constant current and the current requirements (thus total power requirements) are much higher than those of a DS1 NIU.
A possible solution is to change the SPPM so that several of its 28 powering ports would be “DS3 only.” This approach, however, suffers the disadvantages of losing availability from those “DS3 only” ports for the more common DS1 NIU application and could result in the destruction of a DS1 NIU should it be inadvertently connected to a DS3-designated powering port. This is unacceptable in practice.
Another possible solution changes the SPPM to incorporate a span power supply that powers either a DS3 NIU or DS1 NIU using a user-accessible switch that allows a user to select a desired mode of operation. This switchable-mode, span power supply would be used in several of the 28 ports with the original DS1-only span power supply used in the remaining ports. This approach, however, is not automatic and requires direct user intervention. Also, as a further disadvantage, a DS1 NIU could be destroyed, if the user does not put the mode-select switch in the appropriate position for the equipment to be powered.